This study is part of a multi-country case-control study to determine causes of and risk factors for severe and very severe pneumonia among children <5 years of age, as defined by the World Health Organization. The study is funded by the Bill &Melinda Gates Foundation and coordinated by a research team at the School of Public Health, Johns Hopkins University. The sites where the study will be conducted are projected to be representative of the areas where most of the severe pneumonia cases in children will occur in 2015 and where key interventions that are expected to be widespread from 2015 onwards are already in place. Seven PERCH sites that have been selected include Johannesburg, South Africa , Lusaka, Zambia, Kilifi, Kenya, Basse, the Gambia, Bamako, Mali, Dhaka, Bangladesh and Sa Kaeo and Nakhon Phanom, Thailand. In Thailand, the study will be implemented through a collaboration between Ministry of Public Health and the Intemational Emerging Infections Program (lEIP) in two mral provinces: Sa Kaeo and Nakhon Phanom. Sa Kaeo province is in eastem Thailand on the Cambodian border and has a population of 537,000 (32,000 age <5 years). Nakhon Phanom borders Laos in northeastem Thailand and has 742,000 residents (48,000 age <5). The 2007 per capita annual GDP was $997 in Sa Kaeo province and $1,006 in Nakhon Phanom province (Information 2007). The PERCH study will be conducted in the provincial hospitals in each province.